1. Field of the Invention
The present invention relates to a circulation member for circulating a number of balls and spacers disposed in a ball rolling passage formed between a track member and a movable member in conformity with a relative motion of the movable member with respect to the track member, and also relates to motion guide device and ball screw provided with such circulation member.
2. Related Art
The applicant of the subject application provided a circulation member such as shown in FIG. 20 applied to a ball screw, which is disclosed in Japanese Patent Application No. HEI 10-180767.
With reference to FIG. 20, a ball screw is formed with a ball rolling groove, and balls 1 rolling along the ball rolling groove contact both edge portions 3a, 3b of a scoop-up groove 3 formed in a circulation member 2 and are then scooped from the ball rolling groove 3 in an embraced fashion. In the case where scoop-up groove 3 is formed in the circulation member 2, an impact force is substantially not applied to the circulation member 2, and therefore, it becomes possible to rotate a screw shaft at high speed to thereby move the balls 1 also at high speed.
Such circulation member 2 may be functionally sufficient to act only to circulate the balls 1. However, there are many cases where spacers are disposed between the balls 1 for preventing friction or like. Such a spacer has substantially cylindrical shape having a diameter smaller than that of the ball 1 and is provided, at its both end portions in the ball advancing direction, with recesses in conformity with the spherical shape of the ball.
When scooping the ball 1 and the spacer by using the circulation member of the conventional structure mentioned above, for example, because the ball 1 has a spherical surface, the ball 1 is embraced and scooped by both side edge portions 3a, 3a of the scoop-up groove 3. In a case where there exists a small gap between the adjacent balls 1, 1, the spacer put between the balls 1, 1 may be also scooped together with the balls. However, as shown in FIGS. 21 and 22, in a case where the spacer 4 freely moves between the adjacent balls 1, 1, there is a fear that the spacer 4 engages with the side edge portions 3a, 3b of the scoop-up groove 3 because the spacer 4 has nearly flat end portions in the advancing direction, thus being inconvenient.